package tools

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"time"
)

type DataEmitter func(ctx context.Context) chan interface{}

func SseWrapper(w http.ResponseWriter, r *http.Request, emitter DataEmitter) {
	flusher, ok := w.(http.Flusher)
	if !ok {
		http.Error(
			w,
			"flushing is not allowed",
			http.StatusFailedDependency,
		)
		return
	}

	ctx := r.Context()

	dE := emitter(ctx)

	for {
		select {
		case <-ctx.Done():
			return
		case <-time.After(time.Second * 10):
			SSEPing(w)
		case m := <-dE:
			line, err := json.Marshal(m)
			if err != nil {
				panic(err)
			}

			if _, err := w.Write(
				[]byte(
					fmt.Sprintf(
						"data: %s\n\n",
						string(line),
					),
				),
			); err != nil {
				panic(err)
			}

			flusher.Flush()
		}
	}
}

// Sends SSE ping
func SSEPing(w http.ResponseWriter) {
	if _, err := w.Write([]byte(":ping\n\n")); err != nil {
		panic(err)
	}

	if flusher, ok := w.(http.Flusher); ok {
		flusher.Flush()
	} else {
		panic("streaming unsupported")
	}
}